Numpy's __array_interface__ not returning dict

Question

I am using an external program to compute a matrix that is written in C++ and is interfaced with python through boost::python. I would like to pass this C array to numpy, and according to the authors this ability is already implemented with numpy's obj.__array_interface__. If I call this in a python script and assign the C++ object to X I obtain the following:

print X
#<sprint.Matrix object at 0x107c5c320>

print X.__array_interface__
#<bound method Matrix.__array_interface__ of <sprint.Matrix object at 0x107c5c320>>

print X.__array_interface__()
#{'shape': (5, 5), 'data': (4416696960, True), 'typestr': '<f8'}

print np.array(X)
#Traceback (most recent call last):
#  File "<string>", line 96, in <module>
#ValueError: Invalid __array_interface__ value, must be a dict

From my limited understanding I believe the problem is X.__array_interface__ is not actually returning anything without the (). Is there a way to pass these arguments to np.array explicitly or a workaround for this issue.

I am really quite new to mixing C++ and python, if this makes no sense or if I need to expound on any part let me know!

Answer 1

__array_interface__ should be a property (instance variable), not a method. So in the C++, or wherever the 'sprint.Matrix' object is defined, change it so that instead of having:

print X.__array_interface__
#<bound method Matrix.__array_interface__ of <sprint.Matrix object at 0x107c5c320>>

you have

print X.__array_interface__
#{'shape': (5, 5), 'data': (4416696960, True), 'typestr': '<f8'}

An alternative would be to define a custom wrapper class:

class SprintMatrixWrapper(object):
    def __init__(self, sprint_matrix):
        self.__array_interface__ = sprint_matrix.__array_interface__()

and then simply do:

numpy.array(SprintMatrixWrapper(X))